JP5194590B2 - Engine exhaust purification system - Google Patents

Description

  The present invention relates to an engine exhaust purification device that executes a fuel addition process for supplying an unburned fuel component to a catalyst provided in an exhaust passage.

2. Description of the Related Art As an engine exhaust gas purification device, a device provided with a NOx occlusion reduction catalyst for purifying nitrogen oxide (NOx) contained in exhaust gas as described in Patent Document 1 is known.
This NOx occlusion reduction catalyst occludes NOx in a state where oxygen is excessive with respect to the fuel injection amount, so-called lean state. On the other hand, in a state where oxygen is insufficient with respect to the fuel injection amount, that is, a so-called rich state, carbon monoxide (CO) and unburned fuel component hydrocarbons (HC) contained in the exhaust and stored NOx are reduced. The exhaust gas is purified by reacting to reduce NOx and converting them into nitrogen, carbon dioxide, and water.

By the way, the NOx occlusion reduction catalyst has a limit in the occlusion amount of NOx, and the occlusion amount of NOx increases with engine operation, and the ability to occlude NOx decreases as it approaches a saturated state. Thus, in an exhaust purification device equipped with such a NOx occlusion reduction catalyst, the catalyst is occluded by executing a fuel addition process for adding fuel to the exhaust and temporarily setting the atmosphere in the vicinity of the catalyst to a rich state. Reduction of NOx storage capacity is suppressed by reducing NOx. In addition, as a method of such fuel addition processing, a fuel addition valve is provided in a portion upstream of the catalyst in the exhaust passage, and fuel is injected from the fuel addition valve. A method of performing post injection in which fuel is injected from the fuel injection valve during the exhaust stroke is employed.
JP 2006-291837 A

  By the way, in the exhaust emission control device for an engine that executes such fuel addition processing, when the exhaust gas flow rate is large, the unburned fuel component added to the exhaust gas may pass through the catalyst without being completely reacted. In such a case, the unburned fuel component becomes white smoke from the exhaust pipe and is discharged into the atmosphere.

  Such a problem is not limited to the above-described exhaust purification device including the NOx storage reduction catalyst. For example, a catalyst function is added to a filter that captures particulate matter (hereinafter referred to as PM) contained in exhaust gas. Exhaust gas purification that performs fuel addition processing to supply unburned fuel components to the catalyst provided in the exhaust passage, such as those that oxidize and remove PM deposited on the filter with its reaction heat by supplying fuel fuel components The devices are generally common.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an engine exhaust capable of suppressing unburned fuel components from passing through the catalyst while remaining unreacted to become white smoke and discharged into the atmosphere. It is to provide a purification device.

In the following, means for achieving the above object and its effects are described.
According to a first aspect of the present invention, there is provided an exhaust gas purification apparatus for an engine that executes a fuel addition process for supplying an unburned fuel component to a catalyst provided in an exhaust passage, and includes a catalyst bed temperature estimating means for estimating the temperature of the catalyst The fuel addition process is prohibited when the exhaust flow rate is equal to or higher than a reference exhaust flow rate set based on the catalyst bed temperature estimated by the catalyst bed temperature estimation means, and the reference exhaust flow rate is The gist is that the lower the catalyst bed temperature estimated by the temperature estimating means, the smaller the value is set .

  When the catalyst bed temperature is high, the reaction of the unburned fuel component in the catalyst is promoted, so that the reaction is completed in a short period of time. On the other hand, when the catalyst bed temperature is low, the reaction rate of the unburned fuel component in the catalyst is relatively small. Therefore, when the exhaust gas flow rate is high, that is, when the flow rate of the exhaust gas passing through the catalyst is high, the unburned fuel component that could not be reacted. It will pass through the catalyst. Therefore, in the first aspect of the present invention, the reference exhaust flow rate is set based on the catalyst bed temperature, and the fuel addition process is prohibited when the exhaust flow rate is equal to or higher than the reference exhaust flow rate. That is, when there is a possibility that unburned fuel components pass through the catalyst and are discharged into the atmosphere, the fuel addition process is prohibited. As a result, it is possible to suppress the unburned fuel component from passing through the catalyst without being reacted and becoming white smoke and being discharged into the atmosphere.

Further, according to the above configuration, the reference exhaust flow rate is set to a smaller value as the catalyst bed temperature is lower and the amount of unburned fuel component that reacts per unit time in the catalyst is smaller. Therefore, the fuel addition process can be prohibited in a manner that is more suitable for the possibility of white smoke .
According to a second aspect of the present invention, there is provided an exhaust purification apparatus for an engine that performs a fuel addition process for supplying an unburned fuel component to a catalyst provided in an exhaust passage, and further comprises a catalyst bed temperature estimating means for estimating a temperature of the catalyst. And when the exhaust flow rate is equal to or higher than a reference exhaust flow rate set based on the catalyst bed temperature estimated by the catalyst bed temperature estimation means, the fuel addition process is prohibited, and the reference exhaust flow rate is a fuel addition amount. The gist is that the smaller the value is, the smaller the value is set.
When the catalyst bed temperature is high, the reaction of the unburned fuel component in the catalyst is promoted, so that the reaction is completed in a short period of time. On the other hand, when the catalyst bed temperature is low, the reaction rate of the unburned fuel component in the catalyst is relatively small. Therefore, when the exhaust gas flow rate is high, that is, when the flow rate of the exhaust gas passing through the catalyst is high, the unburned fuel component that could not be reacted. It will pass through the catalyst. Therefore, in the invention described in claim 2, the reference exhaust flow rate is set based on the catalyst bed temperature, and the fuel addition process is prohibited when the exhaust flow rate is equal to or higher than the reference exhaust flow rate. That is, when there is a possibility that unburned fuel components pass through the catalyst and are discharged into the atmosphere, the fuel addition process is prohibited. As a result, it is possible to suppress the unburned fuel component from passing through the catalyst without being reacted and becoming white smoke and being discharged into the atmosphere.
Here, even when the exhaust gas flow rate and the catalyst bed temperature are the same, when the amount of fuel added is large, there is a high possibility that the added unburned fuel component will not react and pass through the catalyst. Therefore, as described in the second aspect of the invention, by adopting a configuration in which the reference exhaust flow rate is set to a smaller value as the fuel addition amount increases, the fuel addition process increases as the fuel addition amount increases. This increases the chances that the fuel addition is prohibited, and the fuel addition process can be suitably prohibited in a manner in accordance with the possibility that the unburned fuel component is discharged into the atmosphere.
The invention of claim 3 is the invention according to claim 2, to set the reference exhaust flow rate as when the catalyst bed temperature is low to a small value.

  According to the third aspect of the present invention, the reference exhaust flow rate is set to a smaller value as the catalyst bed temperature is lower and the amount of unburned fuel component that reacts per unit time in the catalyst is smaller. Therefore, the fuel addition process can be prohibited in a manner that is more suitable for the possibility of white smoke.

  According to a fourth aspect of the present invention, in the exhaust emission control device for an engine according to any one of the first to third aspects, an upstream side exhaust temperature sensor provided at a site upstream of the catalyst in the exhaust passage. And a downstream side exhaust temperature sensor provided at a downstream side of the catalyst, and the catalyst bed temperature estimation means includes a lower exhaust temperature among the exhaust temperatures detected by the respective exhaust temperature sensors. The gist is to estimate the catalyst bed temperature based on the above.

  The temperature of the catalyst varies depending on the heat of reaction of the unburned fuel component and heat exchange with the exhaust gas that passes through the catalyst. Become. For this reason, the catalyst bed temperature is hardly uniform over the entire catalyst, and a temperature difference depending on the part is likely to occur. Therefore, in the invention described in claim 4, exhaust temperature sensors are provided in the upstream and downstream portions of the catalyst in the exhaust passage, and the lower exhaust temperature of the exhaust temperatures detected by each exhaust temperature sensor. Is used to estimate the catalyst bed temperature, and the reference exhaust gas flow rate is set based on the estimated catalyst bed temperature. The exhaust temperature detected by the upstream exhaust temperature sensor changes with a high correlation with the temperature of the upstream portion of the catalyst. On the other hand, the exhaust temperature detected by the downstream exhaust temperature sensor changes with a high correlation with the temperature of the downstream portion of the catalyst. Therefore, according to the configuration described in claim 4, even when the catalyst bed temperature is uneven between the upstream portion and the downstream portion of the catalyst, and there is a low temperature portion of the catalyst, The reference exhaust flow rate can be set based on the reaction rate of the unburned fuel component at the low temperature portion, and the unburned fuel component can be more preferably suppressed from being discharged into the atmosphere. It becomes like this.

The invention according to claim 5 is the engine exhaust gas purification apparatus according to any one of claims 1 to 4 , wherein the catalyst is a NOx occlusion reduction catalyst that occludes nitrogen oxides contained in the exhaust gas. The NOx occlusion amount of the NOx occlusion reduction catalyst is estimated based on the engine operating state and the fuel addition amount, and when the estimated NOx occlusion amount is equal to or greater than a predetermined amount, the fuel addition process is executed to perform the NOx occlusion. The gist is to supply the unburned fuel component to the reduction catalyst as a reducing agent and to reduce the nitrogen oxides stored in the NOx storage reduction catalyst.

  In an exhaust emission control device that includes a NOx occlusion reduction catalyst that occludes nitrogen oxide (NOx) contained in exhaust gas, the amount of NOx contained in the exhaust gas, that is, the NOx occlusion reduction catalyst, is occluded based on the engine operating state. Estimate the amount of NOx, estimate the amount of NOx that is reduced by the reduction reaction in the catalyst based on the amount of fuel added, and estimate the current NOx storage amount based on the integrated values of these stored amounts and the reduced amount doing.

Here, for example, in order to suppress the unburned fuel component added to the exhaust gas from passing through the catalyst and being discharged into the atmosphere, the fuel addition process is not prohibited, but the fuel addition is performed as the exhaust gas flow rate increases. Although a configuration in which the amount is reduced can be adopted, in such a configuration, a small amount of fuel addition is repeatedly performed. And when estimating the slight reduction amount by such a small amount of fuel addition, the influence which an estimation error has with respect to the estimated value becomes comparatively large. Therefore, when a small amount of fuel addition is repeated, such estimation errors are integrated, and the reliability of the estimation result of the NOx occlusion amount is lowered. On the other hand, in the exhaust emission control device that estimates the NOx occlusion amount based on the engine operating state and the fuel addition amount, as in the invention described in the fifth aspect , the invention described in the first to fourth aspects. In the case of adopting the configuration, by prohibiting the fuel addition process when the exhaust gas flow rate is equal to or higher than the reference exhaust gas flow rate, it is possible to suppress such a decrease in reliability of the NOx occlusion amount estimation result. .

A sixth aspect of the present invention is the engine exhaust gas purification apparatus according to any one of the first to fifth aspects, wherein a fuel addition valve is provided in the exhaust passage, and the fuel addition valve is provided during the fuel addition process. The main point is to add the fuel to the exhaust gas by injecting the fuel.

As a specific method for adding fuel into the exhaust during fuel addition process, such as by the invention of claim 6, the fuel addition valve provided in an exhaust passage, the exhaust by injecting fuel from the fuel addition valve A method of adding fuel can be employed.

  By the way, a part of the injected fuel may remain attached around the nozzle hole of the fuel addition valve. When the fuel addition valve is hot due to exhaust heat, the fuel attached to the periphery of the nozzle hole changes in quality due to the heat, and the viscosity becomes high, and it gradually accumulates and deposits block a part of the nozzle hole. There is a risk that. As the deposit builds up, it becomes difficult to perform appropriate fuel addition.

As described above, when the exhaust gas flow rate is large, the fuel addition process is not prohibited, and if the amount is reduced to suppress the generation of white smoke, a small amount of injection is repeatedly executed. Become so. When the injection amount is large, the temperature around the nozzle hole is lowered due to the cooling effect associated with fuel injection, so the fuel adhering to the nozzle hole is unlikely to deteriorate, but this cooling is necessary when a small amount of injection is performed. Since the action is small, deposit deposition is relatively easy to proceed. Therefore, when the unburned fuel component is supplied to the catalyst by the fuel addition valve as in the invention described in claim 6 , the invention described in claims 1 to 5 is applied and the exhaust flow rate is applied. When there is a large amount of fuel, it is desirable to adopt a configuration that prohibits fuel addition.

According to a seventh aspect of the invention, in the exhaust emission control device for an engine according to the sixth aspect , when a predetermined period or more has elapsed from the most recent fuel injection by the fuel addition valve, a predetermined amount of fuel is supplied from the fuel addition valve. The gist of the present invention is to execute the clogging prevention injection process.

Further, in the exhaust emission control device provided with the fuel addition valve in the exhaust passage as in the invention described in claim 6 , the predetermined fuel injection from the latest fuel injection in the fuel addition valve is determined as in the invention described in claim 7. A configuration in which a clogging prevention injection process of injecting a predetermined amount of fuel from the fuel addition valve when the period has elapsed can be employed. Thereby, the deposit adhering to the periphery of the nozzle hole by the fuel injection from the fuel addition valve can be removed, and the occurrence of clogging of the fuel addition valve due to the deposit can be suppressed.

  By the way, as described above, in order to suppress the generation of white smoke, it is possible not to prohibit the fuel addition process but to adopt a configuration in which the fuel addition amount is reduced when the exhaust flow rate is large. In the case where the injection amount associated with is small, even if fuel injection by the fuel addition valve is executed, the deposit may be hardly removed. Therefore, in such a case, the clogging prevention injection cannot be performed at an appropriate time, and there is a possibility that a state in which a large amount of deposit is accumulated in the injection hole of the fuel addition valve continues for a long period of time.

In this regard, as in the seventh aspect of the invention, in the exhaust purification device that prohibits the fuel addition processing when the exhaust flow rate is equal to or higher than the reference exhaust flow rate, when fuel injection by the fuel addition valve is not executed for a predetermined period of time. According to the configuration for performing the clogging prevention injection, the clogging prevention injection can be executed in a manner corresponding to the occurrence of the clogging of the fuel addition valve based on the presence or absence of the fuel injection accompanying the fuel addition processing. become.

Hereinafter, an embodiment in which an exhaust emission control device for an engine according to the present invention is embodied in an exhaust emission control device for a diesel engine will be described with reference to FIGS.
FIG. 1 is a schematic diagram showing a schematic configuration of a diesel engine 10 and its exhaust purification device according to the present embodiment. As shown in FIG. 1, an intake passage 20 and an exhaust passage 30 are connected to the diesel engine 10. The intake passage 20 is provided with an intake throttle valve 21 that is opened and closed by a motor 21a. By changing the opening of the intake throttle valve 21, the amount of air introduced into the combustion chamber 11 is adjusted. The

  The combustion chamber 11 of the diesel engine 10 is provided with a fuel injection valve 12 for each cylinder. These fuel injection valves 12 are connected to a common rail 13 and inject fuel filled in the common rail 13 into the combustion chamber 11. The common rail 13 is supplied with fuel by a supply pump 14.

  As shown in FIG. 1, the intake passage 20 and the exhaust passage 30 are connected to a turbocharger 22. The turbocharger 22 rotates the turbine 22 a with the energy of the exhaust gas flowing through the exhaust passage 30 to pressurize the air in the intake passage 20 and send it into the combustion chamber 11.

  A catalytic converter 41 and a PM filter 42 are provided in the exhaust passage 30. These catalytic converter 41 and PM filter 42 carry a NOx storage reduction catalyst. This NOx occlusion reduction catalyst occludes NOx in a state where oxygen is excessive with respect to the fuel injection amount, so-called lean state. On the other hand, in a state where oxygen is insufficient with respect to the fuel injection amount, that is, a so-called rich state, carbon monoxide (CO) and unburned fuel component hydrocarbons (HC) contained in the exhaust and stored NOx are reduced. The exhaust gas is purified by reacting to reduce NOx and converting them into nitrogen, carbon dioxide, and water.

  The PM filter 42 is formed of a porous material, and thereby captures particulate matter (PM) mainly composed of soot in the exhaust gas. Further, the PM trapped by the PM filter 42 is oxidized and removed by the oxidizing action of the NOx storage reduction catalyst.

  A fuel addition valve 40 that injects fuel into the exhaust gas and supplies HC as an unburned fuel component to the catalytic converter 41 and the PM filter 42 is provided in a portion of the exhaust passage 30 upstream of the catalytic converter 41. Yes. The fuel addition valve 40 is connected to the supply pump 14, and fuel is supplied from the supply pump 14.

  The addition of fuel to the exhaust gas through the fuel addition valve 40 is performed by an electronic control unit 50 that comprehensively executes various controls of the diesel engine 10 as will be described later. The electronic control device 50 includes an air flow meter 51 for detecting the intake air amount GA, a rotational speed sensor 52 for detecting the engine rotational speed NE, and a vehicle speed for detecting the vehicle speed SPD as various sensors for detecting the engine operating state and the vehicle running state. From a sensor 53, an accelerator opening sensor 54 that detects the amount of depression of the driver's accelerator pedal, an upstream exhaust temperature sensor 55 provided upstream of the PM filter 42 in the exhaust passage 30, and a PM filter 42 in the exhaust passage 30 Also, a downstream exhaust temperature sensor 56 provided on the downstream side is connected, and detection signals of these various sensors are taken in.

  The electronic control unit 50 performs calculations based on detection signals taken from these various sensors 51 to 56, and controls each part of the engine. For example, the target fuel injection amount for generating the engine torque according to the driver's request is calculated based on the amount of depression of the accelerator pedal with respect to the detected engine speed NE. Then, the fuel injection valve 12 is controlled so that the fuel injection amount matches the target fuel injection amount.

  Further, the NOx occlusion reduction catalyst has a limit in the occlusion amount of NOx, and the occlusion amount of NOx increases with engine operation, and the ability to occlude NOx decreases as it approaches a saturated state. Therefore, the electronic control unit 50 estimates the NOx occlusion amount of the NOx occlusion reduction catalyst, and executes the fuel addition process for adding fuel to the exhaust through the fuel addition valve 40 as described above when the NOx occlusion amount exceeds a predetermined amount. In addition, the atmosphere near the catalyst is temporarily made rich to reduce NOx occluded by the catalyst, thereby suppressing a decrease in NOx occlusion capacity.

  Specifically, the amount of NOx contained in the exhaust, that is, the amount of NOx occluded in the NOx occlusion reduction catalyst is estimated based on the engine operating state such as the engine speed NE and the fuel injection amount, and the amount of fuel added The amount of NOx that is reduced by the reduction reaction in the catalyst is estimated based on the above, and the current NOx storage amount is estimated based on the integrated values of these stored amounts and the reduced amount. When the NOx occlusion amount becomes equal to or greater than the predetermined amount, fuel addition processing is performed in which fuel is injected from the fuel addition valve 40 and unburned fuel component HC is supplied as a reducing agent to the NOx occlusion reduction catalyst.

  By the way, when such a fuel addition process is executed, when the exhaust gas flow rate is high, that is, when the exhaust gas flow rate is high, the added HC passes through the catalyst before it completely reacts in the NOx storage reduction catalyst. There is a case. In such a case, HC as an unburned fuel component is discharged from the exhaust pipe to the atmosphere, and in some cases, white smoke may be generated.

  Therefore, in the exhaust purification device of the present embodiment, the fuel addition process is prohibited when the exhaust gas flow rate is large. Hereinafter, with reference to FIG.2 and FIG.3, the prohibition aspect of this fuel addition process is demonstrated in detail. FIG. 2 is a flowchart showing a flow of a series of processes related to the fuel addition process. This process is repeatedly executed at a predetermined control cycle by the electronic control unit 50 when the estimated NOx storage amount of the NOx storage reduction catalyst becomes a predetermined amount or more.

  As shown in FIG. 2, when this process is started, in step S100, a fuel addition amount Q is calculated based on the fuel injection amount from the fuel injection valve 12 and the engine speed NE. Next, in step S110, the temperature of the PM filter 42 is based on the upstream exhaust temperature THUP detected by the upstream exhaust temperature sensor 55 and the downstream exhaust temperature THLW detected by the downstream exhaust temperature sensor 56. Estimate the catalyst bed temperature THC. Specifically, the lower one of the upstream side exhaust temperature THUP and the downstream side exhaust temperature THLW is set as the catalyst bed temperature THC.

  When the catalyst bed temperature THC is estimated in this way, the process proceeds to step S120, and the reference exhaust flow rate EXst is set based on the catalyst bed temperature THC and the fuel addition amount Q. The calculation of the reference exhaust flow rate EXst is performed with reference to a calculation map stored in advance in the memory of the electronic control unit 50. As shown in FIG. 3, this calculation map has such characteristics that the reference exhaust flow rate EXst is set to a smaller value as the catalyst bed temperature THC is lower and as the fuel addition amount Q is larger. Yes.

  When the reference exhaust flow rate EXst is set with reference to the calculation map shown in FIG. 3, the process proceeds to step S130 to determine whether or not the current exhaust flow rate EX is less than the reference exhaust flow rate EXst. Here, the exhaust flow rate EX is a value calculated on the basis of the value of the intake air amount GA detected by the air flow meter 51. For example, the exhaust flow rate EX is determined taking into account the transport delay of air from the air flow meter 51 to the PM filter 42. It is calculated as a value that changes with a predetermined delay with respect to the change in the intake air amount GA by performing a smoothing process on the value of the air amount GA.

  If it is determined in step S130 that the current exhaust flow rate EX is less than the reference exhaust flow rate EXst (step S130: YES), the process proceeds to step S140, in which fuel is injected from the fuel addition valve 40 and fuel addition processing is performed. Execute. On the other hand, if it is determined in step S130 that the current exhaust flow rate EX is equal to or higher than the reference exhaust flow rate EXst (step S130: NO), step S140 is skipped and fuel injection by the fuel addition valve 40 is not executed. Then, this process is temporarily terminated.

  In the exhaust purification apparatus of the present embodiment, the fuel addition process is prohibited when the exhaust flow rate EX is equal to or higher than the reference exhaust flow rate EXst by repeatedly executing such a process.

According to the embodiment described above, the following effects can be obtained.
(1) Since the reaction of the unburned fuel component (HC) in the catalytic converter 41 and the PM filter 42 is promoted when the temperature of the catalyst is high, the reaction ends in a short period. On the other hand, when the temperature of the catalyst is low, the reaction speed of the unburned fuel component in the catalytic converter 41 and the PM filter 42 is relatively small. Therefore, when the exhaust gas flow rate EX is large, that is, the flow velocity of the exhaust gas passing through the catalytic converter 41 and the PM filter 42. When is large, unburned fuel components that could not be reacted pass through the catalytic converter 41 and the PM filter 42. Therefore, in the above embodiment, the reference exhaust flow rate EXst is set based on the catalyst bed temperature THC, and the fuel addition process is prohibited when the exhaust flow rate EX is equal to or higher than the reference exhaust flow rate EXst. That is, when there is a possibility that unburned fuel components pass through the catalytic converter 41 and the PM filter 42 and are discharged into the atmosphere, the fuel addition process is prohibited. As a result, it is possible to suppress the unburned fuel component from passing through the catalytic converter 41 and the PM filter 42 while remaining unreacted to become white smoke and discharged into the atmosphere.

  (2) In the above embodiment, the reference exhaust flow rate EXst is set to a smaller value as the catalyst bed temperature THC is lower. According to such a configuration, the reference exhaust flow rate EXst is set to a smaller value as the catalyst bed temperature THC is lower and the amount of unburned fuel component that reacts per unit time in the catalytic converter 41 and the PM filter 42 is smaller. Become. Therefore, the fuel addition process can be prohibited in a manner that is more suitable for the possibility of white smoke.

  (3) The temperature of the catalyst varies depending on the reaction heat of the unburned fuel component and heat exchange between the catalytic converter 41 and the PM filter 42 and the exhaust gas passing through the catalyst. The amount of heat exchange varies depending on the site. For this reason, the temperature of the catalyst is rarely uniform throughout the catalytic converter 41 and the PM filter 42, and a temperature difference depending on the part is likely to occur. Therefore, in the above-described embodiment, the exhaust temperature sensors 55 and 56 are provided in the upstream and downstream portions of the PM filter 42 in the exhaust passage 30, and the exhaust temperatures THUP and THLW detected by the exhaust temperature sensors 55 and 56, respectively. Of these, the catalyst bed temperature THC is estimated based on the lower exhaust temperature, and the reference exhaust flow rate EXst is set based on the estimated catalyst bed temperature THC. The upstream exhaust temperature THUP detected by the upstream exhaust temperature sensor 55 changes with a high correlation with the temperature of the upstream portion of the PM filter 42. On the other hand, the downstream exhaust temperature THLW detected by the downstream exhaust temperature sensor 56 changes with a high correlation with the temperature of the downstream portion of the PM filter 42. Therefore, according to the configuration of the above embodiment, even if the catalyst bed temperature THC is uneven between the upstream portion and the downstream portion of the PM filter 42 and there is a low temperature portion, the temperature It becomes possible to set the reference exhaust gas flow rate EXst based on the reaction rate of the unburned fuel component at a low part, so that the unburned fuel component can be more suitably suppressed from being discharged into the atmosphere. become.

  (4) Even when the exhaust gas flow rate EX and the catalyst bed temperature THC are the same, when the fuel addition amount Q is large, there is a possibility that the added unburned fuel component may not react and pass through the catalytic converter 41 and the PM filter 42. Becomes higher. Therefore, by adopting a configuration in which the reference exhaust flow rate EXst is set to a smaller value as the fuel addition amount Q is larger as in the above embodiment, the fuel addition process is prohibited as the fuel addition amount Q is larger. As a result, the fuel addition process can be suitably prohibited in a manner in accordance with the possibility of unburned fuel components being discharged into the atmosphere.

  (5) In the above embodiment, the amount of NOx contained in the exhaust, that is, the amount of NOx stored in the NOx storage reduction catalyst is estimated based on the engine operating state, and the reduction reaction in the catalyst is performed based on the fuel addition amount. The amount of NOx to be reduced is estimated, and the current NOx storage amount is estimated based on the integrated values of the storage amount and the reduction amount.

  Here, for example, in order to suppress the unburned fuel component added to the exhaust gas from passing through the catalyst and being discharged into the atmosphere, the fuel addition process is not prohibited, but the fuel is increased as the exhaust flow rate EX increases. Although a configuration in which the addition amount Q is reduced can be adopted, in such a configuration, a small amount of fuel is repeatedly added. And when estimating the slight reduction amount by such a small amount of fuel addition, the influence which an estimation error has with respect to the estimated value becomes comparatively large. Therefore, when a small amount of fuel addition is repeated, such estimation errors are integrated, and the reliability of the estimation result of the NOx occlusion amount is lowered. On the other hand, as in the above embodiment, by prohibiting the fuel addition process when the exhaust gas flow rate EX is equal to or higher than the reference exhaust gas flow rate EXst, it is possible to suppress the decrease in reliability of the NOx occlusion amount estimation result. Will be able to.

  (6) A portion of the injected fuel may remain attached around the nozzle hole of the fuel addition valve 40. When the fuel addition valve 40 is at a high temperature due to the exhaust heat, the fuel adhering to the periphery of the nozzle hole changes in quality due to the heat, and the viscosity increases, and the deposit gradually accumulates to block a part of the nozzle hole. There is a risk of it. As the deposit builds up, it becomes difficult to perform proper fuel addition.

  As described above, when the amount of white smoke is suppressed by reducing the fuel addition amount Q without prohibiting the fuel addition processing when the exhaust gas flow rate EX is large, a small amount of injection is performed. It will be executed repeatedly. When the injection amount from the fuel addition valve 40 is large, the temperature around the nozzle hole is lowered by the cooling action accompanying the fuel injection, so that the fuel adhering to the nozzle hole is difficult to change, but a small amount of injection is performed. In such a case, such a cooling action is small, and deposit deposition is relatively easy to proceed. Therefore, as in the above-described embodiment, when the unburned fuel component is supplied to the catalyst by the fuel addition valve 40, it is desirable to adopt a configuration in which the fuel addition process is prohibited when the exhaust flow rate EX is large. .

In addition, the said embodiment can also be implemented with the following forms which changed this suitably.
A configuration in which a clogging prevention injection process of injecting a predetermined amount of fuel from the fuel addition valve 40 when a predetermined period or more has elapsed since the latest fuel injection in the fuel addition valve 40 may be employed. Thereby, the deposit adhering to the periphery of the injection hole by the fuel injection from the fuel addition valve 40 can be removed, and the occurrence of clogging of the fuel addition valve 40 due to the deposit can be suppressed.

  By the way, in order to suppress the generation of white smoke as described above, the fuel addition process is not prohibited, but the fuel addition amount Q is decreased when the exhaust flow rate EX is large, and the fuel injection amount by the fuel addition valve 40 is reduced. It is possible to adopt a configuration in which the amount is reduced. However, when the injection amount accompanying the fuel addition is small, even if the fuel injection by the fuel addition valve 40 is executed, the deposit may be hardly removed. Therefore, in such a case, the clogging prevention injection cannot be performed at an appropriate time, and there is a possibility that a state in which a large amount of deposit is accumulated in the injection hole of the fuel addition valve 40 continues for a long period of time.

  In this regard, in the exhaust purification device that prohibits the fuel addition process when the exhaust flow rate EX is equal to or higher than the reference exhaust flow rate EXst as described above, the clogging prevention injection is executed when the fuel injection by the fuel addition valve 40 is not executed for a predetermined period. According to this configuration, the clogging prevention injection can be executed in a manner corresponding to the occurrence of the clogging of the fuel addition valve 40 based on the presence or absence of the fuel injection accompanying the fuel addition process.

  In the above embodiment, the fuel is injected from the fuel addition valve 40 provided in the exhaust passage 30 to supply the unburned fuel component to the NOx occlusion reduction catalyst supported by the catalytic converter 41 and the PM filter 42. Indicated. On the other hand, the method of supplying fuel to the NOx storage reduction catalyst can be changed as appropriate. For example, instead of the method of providing the fuel addition valve 40, after normal fuel injection, a method of performing post injection that injects fuel during the exhaust stroke from the fuel injection valve 12, or the amount of fuel injection from the fuel injection valve 12 For example, a method of executing a rich spike that makes the vicinity of the catalyst rich by increasing the amount of the catalyst can be employed. Also, a method of executing these methods in combination can be employed.

  -In above-mentioned embodiment, although the structure provided with a NOx storage-reduction catalyst was shown as a catalyst, it is not restricted to a NOx storage-reduction catalyst, Other catalysts which require fuel addition processes, such as an oxidation catalyst which oxidizes an unburned fuel component The present invention can be applied to any exhaust purification device that includes the above. For example, an oxidation catalyst is supported on a filter that captures PM contained in the exhaust, a catalytic function is added, and unburned fuel components are supplied to oxidize and remove PM deposited on the filter with its reaction heat. It can also be applied to things that do.

  In the above embodiment, the configuration is shown in which the reference exhaust flow rate EXst is set to a smaller value as the fuel addition amount Q increases. However, the reference exhaust flow rate EXst is set based only on the catalyst bed temperature THC, regardless of the fuel addition amount Q. It can also be set. Even when such a configuration is adopted, it is possible to inhibit the fuel addition process in a manner in accordance with the reaction rate of the unburned fuel component in the PM filter 42 based on the catalyst bed temperature THC and suppress the generation of white smoke. it can.

  In the above embodiment, as the catalyst bed temperature estimating means, the upstream side exhaust temperature sensor 55 and the downstream side exhaust temperature sensor 56 are provided on the upstream side and the downstream side of the PM filter 42 in the exhaust passage 30, respectively. , 56 shows a configuration in which the catalyst bed temperature THC of the PM filter 42 is estimated based on the lower one of the exhaust temperatures detected by. On the other hand, the configuration of the catalyst bed temperature estimating means can be changed as appropriate. For example, the arrangement of the exhaust temperature sensor can be changed as appropriate. Further, a temperature sensor that directly detects the temperature of the PM filter 42 or the catalytic converter 41 can be provided as the catalyst bed temperature estimating means. In this case, it is desirable to employ a configuration in which a plurality of temperature sensors are provided and the reference exhaust flow rate EXst is set based on the lowest temperature among the temperatures detected by the plurality of temperature sensors.

  Further, when the reference exhaust flow rate EXst is set based on the average value Ave = (a1 + a2 +... An / n) of the detection values a by the plurality of temperature sensors, or the lower temperature of the detection values a is weighted. Reference exhaust based on the temperature obtained (for example, temperature A = k1 · a1 + k2 · a2 + ... kn · an / n, [k1> k2> ...> kn, a1> a2> ...> an]) The flow rate EXst can also be set.

  When the catalyst bed temperature THC is sufficiently high, the reaction rate by the NOx occlusion reduction catalyst is sufficiently high, and there is a possibility that white smoke is not generated even when the exhaust gas flow rate is large. In such a case, a configuration is adopted in which the reference exhaust flow rate EXst is set only when the catalyst bed temperature THC is lower than the predetermined temperature, and the fuel addition process is prohibited when the exhaust flow rate EX is equal to or higher than the reference exhaust flow rate EXst. You can also.

  Further, when the catalyst bed temperature THC is lower than the predetermined temperature, a predetermined reference exhaust flow rate (fixed value) that does not depend on the catalyst bed temperature THC is set, and the exhaust flow rate EX is equal to or higher than the reference exhaust flow rate (fixed value). A configuration in which the fuel addition process is sometimes prohibited may be employed.

  In the above embodiment, an example in which the engine exhaust gas purification apparatus according to the present invention is embodied as an exhaust gas purification apparatus for a diesel engine has been described. However, the present invention relates to an unburned fuel component in a catalyst provided in the exhaust passage of the engine. The present invention can be applied to any exhaust gas purification device that executes a fuel addition process for supplying fuel. For example, the present invention can be applied to an exhaust gas purification device for a gasoline engine.

1 is a schematic diagram showing a schematic configuration of a diesel engine and an exhaust purification device according to an embodiment of the present invention. The flowchart which shows the flow of a series of processes concerning the fuel addition process concerning the embodiment. The graph which shows the relationship between a reference | standard exhaust flow volume, catalyst bed temperature, and fuel addition amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Diesel engine, 11 ... Combustion chamber, 12 ... Fuel injection valve, 13 ... Common rail, 14 ... Supply pump, 20 ... Intake passage, 21 ... Intake throttle valve, 21a ... Motor, 22 ... Turbocharger, 22a ... Turbine, 30 DESCRIPTION OF SYMBOLS ... Exhaust passage, 40 ... Fuel addition valve, 41 ... Catalytic converter, 42 ... PM filter, 50 ... Electronic control unit, 51 ... Air flow meter, 52 ... Rotational speed sensor, 53 ... Vehicle speed sensor, 54 ... Accelerator opening sensor, 55 ... upstream exhaust temperature sensor, 56 ... downstream exhaust temperature sensor.

Claims (7)

In an exhaust emission control device for an engine that performs a fuel addition process for supplying an unburned fuel component to a catalyst provided in an exhaust passage,
A catalyst bed temperature estimating means for estimating the temperature of the catalyst;
When the exhaust flow rate is equal to or higher than a reference exhaust flow rate set based on the catalyst bed temperature estimated by the catalyst bed temperature estimation means, the fuel addition process is prohibited ,
The engine exhaust gas purification apparatus , wherein the reference exhaust gas flow rate is set to a smaller value as the catalyst bed temperature estimated by the catalyst bed temperature estimating means is lower . In an exhaust emission control device for an engine that performs a fuel addition process for supplying an unburned fuel component to a catalyst provided in an exhaust passage,
A catalyst bed temperature estimating means for estimating the temperature of the catalyst;
When the exhaust flow rate is equal to or higher than a reference exhaust flow rate set based on the catalyst bed temperature estimated by the catalyst bed temperature estimation means, the fuel addition process is prohibited,
The engine exhaust gas purification apparatus is characterized in that the reference exhaust gas flow rate is set to a smaller value as the fuel addition amount is larger . The exhaust emission control device for an engine according to claim 2 ,
The engine exhaust gas purification apparatus, wherein the reference exhaust gas flow rate is set to a smaller value as the catalyst bed temperature estimated by the catalyst bed temperature estimating means is lower. The engine exhaust gas purification apparatus according to any one of claims 1 to 3,
An upstream exhaust temperature sensor provided at a site upstream of the catalyst in the exhaust passage, and a downstream exhaust temperature sensor provided at a site downstream of the catalyst,
The exhaust gas purifying apparatus for an engine, wherein the catalyst bed temperature estimating means estimates the catalyst bed temperature based on an exhaust gas temperature lower than an exhaust gas temperature detected by each exhaust gas temperature sensor. The catalyst is a NOx occlusion reduction catalyst that occludes nitrogen oxides contained in exhaust gas,
The NOx occlusion amount of the NOx occlusion reduction catalyst is estimated on the basis of the engine operating state and the fuel addition amount, and the NOx occlusion reduction is performed by executing the fuel addition process when the estimated NOx occlusion amount is a predetermined amount or more. The engine exhaust gas purification apparatus according to any one of claims 1 to 4 , wherein an unburned fuel component is supplied to the catalyst as a reducing agent to reduce nitrogen oxides stored in the NOx storage reduction catalyst. A fuel addition valve is provided in the exhaust passage,
The engine exhaust gas purification apparatus according to any one of claims 1 to 5 , wherein fuel is added to exhaust gas by injecting fuel from the fuel addition valve during the fuel addition process. The engine exhaust gas purification apparatus according to claim 6 ,
An engine exhaust gas purification apparatus that executes a clogging prevention injection process in which a predetermined amount of fuel is injected from the fuel addition valve when a predetermined period or more has elapsed since the most recent fuel injection by the fuel addition valve.

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